Battlemechs are cool, but hard to justify in realistic setting. Being upright makes them easier targets. The shape makes them harder to armor compared to a more or less box shaped tank. The propulsion system and controls are unnecessarily complicated.Battlemechs would be fine if plausibly explained:
-> heavy armor would make the ground pressure of their feet way too high, and make their knees/joints either very bulky or very vulnerable!
they are easy to spot, have limited speed (2 steps per second, 5m each = 10m/s = only 36km/h !!!!), and so on...
So a C&C "Titan" style mech is nothing for me.
But I would be totally fine with a walking robot that's not much bigger or heavier than a T-rex or mammoth, rather smaller and relies on stealth and mobility in difficult terrain rather than heavy armor. It could support infantry with heavier firepower than a man could carry (HMG, stingers,...) while following them through forests or mountainous area unsuitable for any wheeled/tracked vehicle.
gameplaywise, this unit would fit better if tanks actually had a disadvantage in forests or hills, like they have in real life. In Civ4 it's not really the case...
Battlesuits/armored exoskeleton are more plausible as extensions of personal body armor. I wouldn't mind seeing those if the game goes that far in future era. IMO, t's more SMAC type material, though.